The prior art is well aware of the use of simple thermocouple structures in glass bending furnaces for the purpose of controlling the temperature within the furnace. Such thermocouple structures are normally inserted in the glass bending furnace through the roof or the side wall of the furnace to provide a temperature control signal. The temperature control signal is processed by other control equipment in order to control radiant heat generating devices within the furnace which supply heat to the furnace.
The thermocouple structures of the prior art, however, are affected by a number of different conditions within the glass bending furnace and thus do not generally accurately indicate the heat which is being generated by the radiant heat generating devices for heating the interior of the glass bending furnace. For example, the following conditions within the glass bending furnace can affect the temperature reported by the prior art thermocouple structures. Randomly generated air currents which result because of temperature differences between different portions of the glass bending furnace cause deviation in temperature readings by the prior art thermocouples. Bending fixtures passing through the glass bending furnace without any glass supported thereon can affect the temperature conditions within the bending furnace and can cause some inaccuracy in the temperature read by the prior art thermocouples. Other processing conditions such as extensive gaps between bending fixtures, dummy bending fixtures between actual bending fixtures, and varying glass and fixture sizes for glass bending fixtures being processed through the glass bending furnace can also affect the readings taken by the prior art thermocouples. Similarly, thermocouples of the prior art type can be affected both by fluctuations in gas burner pressure if gas burners are used as the radiant heat generating devices and by radiant reflection from the glass surfaces of the glass being carried on the bending fixtures.
I set out to design a temperature sensing structure for a glass bending furnace which would accurately detect the radiant energy being generated for heating the interior of the glass bending furnace by a radiant heat generating device. The temperature sensing structure that I wanted to design was one that would not be adversely affected by the changing air currents within the glass bending furnace and by movement of empty bending fixtures, large gaps between bending fixtures, dummy bending fixtures, as well as varying glass and fixture size. I also intended to design an improved temperature sensing structure for a glass bending furnace which would not be adversely affected by fluctuating burner gas pressure when gas burners were used as the radiant heat generating devices or by radiant reflection from glass surfaces passing therethrough.
A search was conducted on the subject matter of this application in the U.S. Patent and Trademark Office. As a result of that search, the following U.S. patents were cited: U.S. Pat. Nos. 2,120,452; 3,123,344; and 3,479,172. While I believe none of the cited patents teach the improved temperature sensing structure of my invention, I will briefly discuss the cited patents below.
U.S. Pat. No. 2,120,452, issued on June 14, 1938, for an "Annealing Lehr." This patent shows an annealing lehr which includes a thermostatic controlling device for automatically maintaining a predetermined temperature for the gases which enter the lehr for heating purposes. In this patent the thermostatic controlling device is identified by the numeral 35. The patent indicates that this device operates an arm 36 connected to an adjustable link 37 and thence to an arm 38 which controls a valve 39 supplying fuel from a pipe 40 to a burner 20. No details are given of the exact makeup of the controlling device 35.
U.S. Pat. No. 3,123,344, issued on March 3, 1964, for "Glass Bending Furnaces." The glass bending furnace shown is of the type generally used today. However, the patent shows only the use of simple thermocouples 42 to detect the temperature within the glass bending furnace. No detailed discussion is made of the exact makeup of the thermocouples 42 other than to indicate that they are thermocouple elements of the type known at the time that glass bending furnace construction was patented.
U.S. Pat. No. 3,479,172, issued on Nov. 18, 1969, for an "Apparatus for Controlling Glass Temperatures." This patent discloses a device for measuring the temperature of a glass sheet as it is conveyed through a lehr or glass bending furnace. A radiation pyrometer is reciprocated transversely of a sheet of glass passing through the bending furnace along a path parallel to and spaced from the sheet of glass. The purpose of using such a traversing radiation pyrometer is to sense directly the temperature of the glass and to transmit the observed temperature profile to conventional recording and temperature control apparatus.